The present invention relates generally to wastewater treatment facilities, and more particularly to trickling filter systems for removing biological nutrients from the wastewater.
Wastewater treatment facilities use a variety of processes for cleaning and treating the wastewater influent they receive. One common process that is used is referred to as a trickling filter process, and one such type of process involves capturing the influent in a clarifying tank for initial processing, passing the influent to an anoxic filter tank for converting nitrates present in the influent into nitrogen gas, and then passing the influent to an oxic filter tank where ammonia can be converted into nitrates. A final clarifying tank is then used to treat any remaining nitrogen and phosphorous compounds before passing the effluent back to lakes, rivers, and other water supplies.
The anoxic stage of the process is most effective when the influent""s exposure to the atmosphere is minimized. However, the influent is generally dumped into the anoxic tank from above, thereby briefly exposing it to atmosphere. After it is dumped into the tank, the influent proceeds to trickle through bacteria-coated media that are submerged in the tank. The bacteria rely on the nitrates and phosphorous in the wastewater for sustenance and then release nitrogen gas into the effluent. A sludge biomass accumulates on the bottom of the tank which further treats the wastewater as it passes therethrough and prior to it passing to the oxic stage of the process.
It is a principal object and advantage of the present invention to provide a system and method for reducing the amount of atmosphere to which wastewater influent is introduced during treatment in an anoxic filter tank.
It is a further object and advantage of the present invention to provide a wastewater treatment system that is energy efficient and therefore cost effective to implement and operate.
It is an additional object and advantage of the present invention to provide a wastewater treatment system that may be retrofit into existing facilities.
Other objects and advantages of the present invention will in part be obvious. And in part appear hereinafter.
In accordance with the foregoing objects and advantages, the present invention provides a two stage process for treating wastewater that subjects the influent to anoxic and oxic filtering processes. The first stage performs anoxic nitrification i.e., the conversion of nitrate to nitrogen gas by bacteria operating in the absence of oxygen. Influent (effluent from the primary clarifiers) is fed into the bottom of the anoxic dentirification tank, preventing contact with the atmosphere and thus reducing the amount of unwanted dissolved oxygen. The influent passes upwards through a layer of sludge biomass before contacting bacteria coated media which performs the denitrification process. This arrangement permits the influent to contact the sludge and the biomass to circulate through the filter, enhancing deoxygenation and the performance of the system.
The denitrified wastewater flows over weirs positioned at the top of the tank where it proceeds to the oxic stage of the process. The second stage involves the use of a traditional trickling filter to convert ammonia to nitrates in the presence of oxygen. This conversion occurs when bacteria coated media comes into contact with the wastewater while being ventilated with oxygen. The nitrates formed during this process are returned to the first stage for the final conversion into nitrogen gas.